This invention relates to the confinement of plasmas by magnetic fields and, more particularly, to a steady-state inductive method for maintaining inductively formed spheromak plasmas.
The spheromak is a compact torus with internal toroidal field and nonlinked coil structure. This topology allows for a simply connected first wall and blanket easing engineering requirements and adding flexibility to reactor concepts by permitting translation and compression. Its very low aspect ratio makes possible a compact high power density reactor core. Its high current density minimizes the need for auxiliary heating. The high ratio of internal to external currents leads to a high engineering beta value, .beta. E, potentially allowing a magnet system using copper coils or pumped liquid metal blanket.
The basic method and apparatus for inductively forming a spheromak plasma is described in U.S. Pat. No. 4,363,776, which is incorporated herein by reference. In accordance with this patent and as shown in FIG. 5, a spheromak plasma is formed by energizing the external equilibrium field coils 5 to produce a first poloidal magnetic field; energizing the poloidal coil in the flux core 2 to produce a second poloidal magnetic field, thereby producing a composite poloidal field which has regions of stronger and weaker strength; energizing the toroidal coil of the flux core to initiate a plasma discharge and to cause toroidal flux to appear outside of the flux core; expanding the plasma in the direction of the region of weaker poloidal magnetic field strength; and pinching off a portion of the expanded plasma by energizing the pinching coils 4 to produce a detached spheromak plasma. U.S. Pat. No. 4,436,691, which is also incorporated herein by reference, is an improvement to the foregoing patent in that it discloses a more efficient means for detaching the spheromak plasma from the flux core and eliminates the need for pinch coils: the directions of the currents in the poloidal field and the toroidal field generating coils are reversed simultaneously such that a resultant normal component V.sub.n of plasma velocity away from the flux core is approximately zero. V.sub.n is determined from the equation: V.sub.n =E.sub.p B.sub.t -E.sub.t B.sub.p where E.sub.t and B.sub.p are the electric and magnetic fields, respectively, produced by the poloidal field generating coil, and where B.sub.t and E.sub.p are the magnetic and electric fields, respectively, produced by the toroidal field generating coil.
While the foregoing inductive method of forming a spheromak plasma offers improvements over other spheromak non-inductive formation methods, the inductive method has not been suitable for continuous or steady-state operation. Inductively produced spheromak plasmas are subject to resistive decay and heretofore the poloidal field and toroidal field have not been able to be maintained, as both are produced (in part or in whole respectively) by plasma currents. The inductive method has been used only in a pulsed operation; i.e. the method must be reproduced at regular intervals.
Steady-state or long-pulse operation of any fusion reactor has many advantages over pulsed operation. Some of these advantages include lower energy, more energy efficiency, less fatigue due to thermal stresses of pulsed operation, and constant power output. The possibility for steady-state operation of spheromaks has relied so far on one of a number of unproven schemes: radio frequency current drive, beam injection, or merging of newly created spheromaks with previously established, but decaying, ones. Steady-state spheromak drive has been proposed by use of electrodes, as well.
Since steady-stae operation is a significant goal in the attainment of a commercial fusion reactor, it is an object of the present invention to provide a steady-state inductive method of maintaining a spheromak plasma.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention.